Respiration of Trichomonas vaginalis. Components detected by electron paramagnetic resonance spectroscopy

Abstract

1. Electron paramagnetic resonance (EPR) spectrometry was used to characterise the iron-sulphur clusters present in the human parasite, Trichomonas vaginalis, an aerotolerant anaerobic protozoan which lacks mitochondria.2. From observations of whole cells and subcellular fractions, the majority of the EPR signals are derived from one of the two main terminal respiration sites, the hydrogenosome; fractionation of hydrogenosomes revealed that a large proportion of these signals were associated with the membrane of these organelles.3. Resolution into eight species was achieved by varying the degree of reduction and the temperature of the samples.4. One component, a [2Fe-2S] ferredoxin reducible by pyruvate : ferredoxin oxidoreductase, corresponds to that previously purified, and predominates in spectra scanned at temperatures higher than 45 K. This species (mid-point redox potential -300 k 20 mV) was detected both in a hydrogenosomal membrane fraction and in the matrix fraction derived from broken organelles.5. Another iron-sulphur species (mid-point potential -270 mV) was detectable in both membrane and matrix at temperatures lower than 30 K.6. Four other reduced species were confined to the hydrogenosomal membrane and a fifth was not detected after subfractionation, although it appeared in intact organelles. This species is assumed to be highly unstable.7. Free-radical signals in hydrogenosome-enriched fractions probably arise from flavoprotein semiquinones; no other signals were obtained from the cytosolic fractions incubated with NADH.8. A signal in the oxidised state was observed in the hydrogenosomal membrane. 9. Possible identities of hydrogenosomal iron-sulphur clusters are discussed in relation to previously established enzyme activities.Trichomonads are parasitic protozoa, which ferment carbohydrates and produce organic acids, H2 and C 0 2 . Although their metabolism is primarily anaerobic, they are aerotolerant [I] and have an active respiratory system [2]. The species studied in greatest detail are the cattle parasite Trichomonas foetus and the sexually transmitted human parasite Trichomonas vaginalis. Neither organism has organelles recognisable in electron micrographs as mitochondria Under aerobic conditions the hydrogenosomes of T. foetusCorrespondence to A. Chapman,

Molecular analysis of the hydrogenosomal ferredoxin of the anaerobic protist Trichomonas vaginalis.

“…One of these comprises putidaredoxin and mitochondrial ferredoxins, which are components of mixed function oxidase systems (10,35,36). Similarities noted in the midpoint potential, optical, and EPR spectra of T. vaginalis ferredoxin (11,13) and of proteins of this family (35,36) already indicated their possible relationship (11), now further supported by characteristic spacing of the first three cysteine residues noted in this study.…”

“…T. vaginalis ferredoxin has a midpoint potential of -320 mV (ref. 13; T.E.G., unpublished results) and an iron-sulfur center with axial symmetry (11,13).…”

Review Article: The hydrogenosome

“…Complex EPR spectra of the isolated organelles indicate that not all hydrogenosomal redox components have yet been recognized (Ohnishi et aE., 1980;Chapman et al, 1986).…”

The Effects of Oxygen on Fermentation in Tritrichomonas Foetus KV1 and its Variant 1MR-100 with Defective Hydrogenosomes

“…Cytochromes are absent from all the trichomonads studied, and it has been argued that a flavoprotein or an iron-sulphur protein are unlikely candidates in this role (Ohnishi et al, 1980;Chapman et al, 1986).…”

“…In the cytosol highly active nicotinamide nucleotide oxidases specific for NADH (Tanabe, 1979) and NADPH (Linstead, 1983), are believed to play an important part in protecting the oxygen-sensitive enzymes of the hydrogenosome. The hydrogenosome itself has a complex chain of flavin and iron-sulphur electron carriers (Ohnishi et al, 1980;Chapman et al, 1986) using either protons or oxygen as terminal electron acceptors. The production of H2 under anaerobic conditions is diminished in Trichomonas vaginalis when 0, is admitted (Lloyd & Kristensen, 1985), and the organism has an intense respiration and shows a high affinity for 0, (Lloyd et al, 1982(Lloyd et al, , 1987Yarlett et al, 1986).…”